The present invention is directed to toner dispensing apparatus. More specifically, the present invention is directed to toner dispensing apparatus for a developer station in an automatic electrostatographic machine. In particular, the invention is specifically directed to the use of a novel toner dispensing roll.
In the art of xerography a photoconductive insulating plate supported by conductive backing is first uniformly charged, and then exposed to a light and shadow image of an image to be reproduced. Under the influence of the light image the photoconductive layer becomes conductive and the charge is selectively dissipated in the light image areas through the photoconductive plate to the conductive backing leaving an electrostatic latent image on the photoconductive plate. The electrostatic latent image which is not visible to the eye is made visible by contacting the photoconductive plate bearing the image with a finely divided pigmented resin base material commonly referred to in the art as toner which is first charged to a potential opposite that of the electrostatic latent image. The toner will adhere to the photoconductive plate in the image or charged areas. Typically the developer is transferred from the photoconductive plate to a final support material such as paper and fixed such as by heat fusing thereto to form a permanent record of the original. The toners employed in this practice are finely divided resin based materials which have an average particle size of about 10 microns. To place a charge on the individual toner particles, the toner is brought in contact with a relatively coarse carrier material which is remote from the carrier in the triboelectric series. During the rubbing and mixing action between the toner and carrier particles, the toner particles become triboelectrically charged to a polarity opposite that of the carrier. Further, the charged toner particles electrostatically coat themselves on the surface of the coarser carrier material and remain bonded thereto in a charged state. To develop an electrostatic latent image this two component material is brought into contact with the photoconductive plate and the toner is electrostatically transferred from the carrier surface to the electrostatic latent image. Thus, the coarser carrier particles not only provide a means for charging the toner particles, but also provide the transportation of the toner particles from one part of the apparatus to the other.
In an automatic reproducing device, the toner material is consumed in the development process and it must be periodically replaced within the development system in order to sustain continuous operation of the machine. Various techniques have been used in the past to replenish the toner supply. Initially new toner material was added directly from supply bottles or containers to the dispensing apparatus by pouring. However, the addition of such gross amounts of toner material altered the triboelectric relationship between the toner and the carrier resulting in reduced charging efficiency of the individual toner particles which accordingly resulted in a reduction in the development efficiency when the developer contacted the latent image bearing surface. Furthermore, the pouring process was both wasteful and dirty in that some of the toner particles became airborne and would tend to migrate into the surrounding area and other parts of the machine. The need to maintain the developer ratio between carrier and toner relatively constant and the need to maintain comparatively uniform triboelectric properties is even more pronounced with the more automatic faster xerographic processing equipment available today. Attempts have been made to provide a separate toner hopper with a dispensing mechanism for adding the toner from the hopper to the developer apparatus in the automatic xerographic reproducing machines on a regular or as needed basis.